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Multicellular organisms use cell division for
- reproduction
- growth
- regeneration (repair of tissues)
Unicellular organisms use cell division primarily for reproduction.
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4 events must occur for cell division:
- reproductive signal: initiates cell division
- replication: of DNA
- segregation: distribution of the DNA into 2 new cells
- cytokinesis: separation of the 2 new cells
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During __, the cell nucleus is visible and cell functions including replication occur.
interphase
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Interphase begins after __ & ends when __ starts.
cytokinesis; mitosis
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3 subphases of interphase
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In __, chromosomes are single, unreplicated structures. There are __ chromosomes.
G1; 46
Neurons will stay in G1 and not divide.
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During __, the DNA replicates; one chromosome becomes 2 sister chromatids.
S phase
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In __, the cell prepares for mitosis. There are now __ chromosomes and __ sister chromatids.
G2; 46; 92
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different DNA sequences that code for the same protein
homologous pairs
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Mitosis and cytokinesis occur during this phase
M phase
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Some cells no longer divide, or divide infrequently and need signals called __ - external chemical signals that stimulate these cells to divide. An example would be __
growth factors; erythropoietin
(Erythropoietin is produced in the kidneys & stimulates division of bone marrow cells and production of red blood cells)
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The DNA molecule is complexed with proteins to form dense __. __ coat DNA - make it compact at the end of G2.
chromatin; condensins
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Packaging of DNA is achieved by __ - proteins with __ charges that attract __ phosphate groups of DNA. Interactions result in the formation of beadlike units, or __
histones; positive; negative; nucleosomes
(page 16 on slide)
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The __ determines the plane of cell division. It __ during __ and will determine spindle orientation.
centrosome; doubles; S phase
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Each __ can consist of __ - hollow tubes formed by microtubules at right angles
centrosome; 2 centrioles
(page 19 and 25 on slide)
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The __ move to opposite ends of the nuclear envelope during G2 to M transition.
centrosomes
(page 25 on slide)
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The sister chromatids are held together by __, which is removed during __ except at the __.
cohesin; prophase; centromere
(page 30 on slide)
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During prophase __, for movement, develop in the __ regions. __ serve as mitotic centers or poles.
kinetochores; centromere; Centrosomes
(page 25 on slide)
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During prophase, microtubules form between the poles to make the spindle. The spindle has 2 types of microtubules:
- polar microtubules: form spindle, overlap in center
- kinetochore microtubules: attach to kinetochores on the chromatids. Sister chromatids attach to opposite halves of the spindle
(page 25 on slide)
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During __, the nuclear envelope breaks down.
prometaphase
(page 27 on slide)
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During __, chromosomes line up at the midline of the cell.
metaphase
46 chromosomes line up one on top of each other.
(page 28 on slide)
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During __, the sister chromatids separate because __ is removed from the centromere. After separation they move to opposite ends of the spindle and are referred to as __
anaphase; cohesin; daughter chromosomes (92)
(page 29 and 30 on slide)
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__ occurs after chromosomes have separated. Spindle breaks down, chromosomes uncoil, nuclear envelope & nucleoli appear. 2 daughter nuclei are formed with identical genetic information.
Telophase
92 daughter chromosomes are splitting into 2 cells each with 46 chromosomes.
(page 32 on slide)
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__ occurs when the plasma membrane pinches between the nuclei because of a contractile ring of microfilaments.
Cytokinesis
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